1. Field of the Invention
The present invention relates to recovery systems for precious metals, and more particularly pertains to a new and improved metals recovery system which utilizes standard cyanide-extraction techniques coupled with carbon adsorption.
2. Description of the Prior Art
There are numerous patents which disclose cyanide extraction and carbon adsorption techniques for precious metals recovery. For example, U.S. Pat. No. 4,177,068, which issued to Balakrishnan, et al. on Dec. 4, 1979, describes a process for the extraction of gold and silver from their ores in which the ore is reduced to a particle size of one millimeter or less and is then mixed with a lixiviant, e.g., an alkaline sodium or potassium cyanide, in an amount to provide a liquor content of about 8 to 12 percent. The lixiviant coated particles are allowed to react for a time sufficient for the lixiviant to extract the noble metal, and the particles are washed with water to obtain a solution of the noble metal salt from which the noble metal is covered. This patent is representative of a number of patents which disclose cyanide extraction techniques for gold and silver.
Another patent of interest is U.S. Pat. No. 4,374,097 which issued to Larry Holland on Feb. 15, 1983. This patent is directed to a method for extracting precious metals from their ores wherein the ore is particulated and mixed with a binding agent to form a paste. The paste material is discharged into a rotary drum at an extruding station where it is pelletized by forcing it through a perforated sidewall of the drum. The pellets are discharged onto a conveyor belt and are transported to a spray station where they are wetted with a lixiviant solution. The lixiviant coated pellets are then dried by exposure to a heated air stream at a drying station while being transported to an open air curing stockpile. The cured pellets are heaped in a pile and are then washed in a water spray to yield a pregnant solution of a precious metal salt.
Also of interest is U.S. Pat. No. 3,920,403 which issued to J. Ross on Nov. 18, 1975. This patent is directed to a method of gold extraction wherein gold in the form of its cyanide complex is desorbed from activated carbon by contacting the carbon with a stripping liquid at a temperature above 130 degrees centigrade but below the decomposition temperature of the gold cyanide complex. The stripping liquid may comprise water, dilute caustic or dilute caustic cyanide.
In recent years, gold and silver extraction techniques which utilize cyanide and carbon adsorption procedures have been refined to the extend that it is now economically feasible to employ these techniques to obtain noble metals from formerly discarded waste materials (often referred to a tailings). More particularly, even the smallest improvements in these existing processes often makes it feasible to recycle such tailings to obtain gold and silver which was not removed during a prior extraction process. As such, there is a continuing need for further refinements to such processes whereby virtually all of the noble metals could be recovered from processed ore and in this respect, the present invention substantially fulfills this need.
In summary, the precious metal recovery system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides a system primarily developed for the purpose of combining cyanide extraction techniques with carbon adsorption, followed by carbon recovery through froth flotation.